Step 1:
The other side of the paper is brown.
Fold in three parts of the same size.

Step 6:
Fold the edges to the centerline.
Then unfold the folds of step 5 and 6

Step 5:
Fold the edges to the centerline

Step 2:
Fold over the upper layer

Step 4:
Prefold in half and turn the model

Step 3:
Fold over the second layer.

Step 10:
Fold over this line

Step 8:
Prefold the edge to the centerline

Step 9:
Prefold, see arrow, use the prefolded lines as guidance

Step 7:
Prefold in half.

Step 16:
Repeat step 14 three more times.

Step 15:
Repeat step 14 here.

Step 12:
Use the prefolded lines as guidance.

Step 11:
Prefold to the prefolded line, see arrow.
Then unfold the fold of step 10

Step 14:
The mountain-fold is already prefolded.
Make the same folds on the other edge.

Step 13:
Fold the edges straight upwards over the prefolded lines.

Step 21:
Make the same folds on the other side.

Step 19:
Fold in half

Step 20:
Fold this corner inwards (make the same fold as the yellow line on the backside).

Step 18:
Fold over the prefolded line, do the same on the other side.

Step 17:
Fold on the corners, do the same on the other side.
Use glue if necessary.

Step 22:
Fold this part in half.

Step 24:
Curve both tentacles.
Press the shell outwards from the inside (if necessary).

Step 23:
Fold this spot to the left